1. Field of the Invention
The present invention relates to a rod antenna and more particularly to a multistage extensible rod antenna system for vehicles equipped with waterproof structure between the antenna rods.
2. Prior Art
In present multistage extensible rod antenna systems for vehicles such as automobiles, a stepped portion is formed at the upper end portion of the outside rod. An elastic sealing ring such as a conductive rubber O-ring, an insulating rubber 0-ring, etc., and collars made of "brass," etc. are fitted into the stepped portion. Then, by processing the end portion of the outside rod with caulking, these sealing rings and collars are press-fitted in order to prevent rain water, etc., from leaking through the interstage space between the outside rod and inside rod.
The foregoing waterproof structure, however, involves a potential risk. During caulking on the end portion of the outside rod, compressive force exceeding the elastic limit of the elastic sealing ring is likely to be applied to it through the collar. In particular, when there is a variation in the dimensions of the processed rod, it is more likely that even greater compressive force will be applied to the elastic sealing ring. If this occurs, the elastic sealing ring loses its elasticity, and the service life of the multistage extensible rod antenna element is drastically shortened.